Interstitial Silica and pH in Marine Sediments: Some Effects of Sampling Procedures

The temperature at which the interstitial water was squeezed from a marine sediment had a profound effect on the measured interstitial silica concentrations which showed an average increase of 51 percent after the sediment was exposed to a temperature 20 degrees C higher than the in situ temperature. Similar effects were not found for interstitial phosphate or alkalinity, but the pH was slightly higher in the water squeezed at the higher temperature. These tempreature-induced changes were completed in a few hours. The use of filter paper can significantly lower the pH of expressed pore waters. Until some important questions about temperature effects are answered, all future data on the pH and silica concentration of pore waters of marine sediments should be obtained from samples extracted at in situ temperatures.